Measurement of the $e^{+}e^{-} \to \eta J/\psi$ cross section and search for $e^{+}e^{-} \to \pi^{0} J/\psi$ at center-of-mass energies between 3.810 and 4.600~GeV

TL;DR

This study measures the cross section of the process e+e- to eta J/psi at various energies between 3.81 and 4.60 GeV, observing significant signals around 4.2 GeV and improving precision over previous measurements.

Contribution

First precise measurement of e+e- to eta J/psi cross section across a broad energy range, confirming an enhancement near 4.2 GeV with improved accuracy.

Findings

Significant signals observed at specific energies around 4.2 GeV.

No signals detected for e+e- to pi0 J/psi.

Energy-dependent cross section shows enhancement near 4.2 GeV.

Abstract

Using data samples collected with the BESIII detector operating at the BEPCII collider at center-of-mass energies from 3.810 to 4.600 GeV, we perform a study of $e^{+}e^{-} \to \eta J/\psi$ and $\pi^0 J/\psi$. Statistically significant signals of $e^{+}e^{-} \to \eta J/\psi$ are observed at $\sqrt{s}$ = 4.190, 4.210, 4.220, 4.230, 4.245, 4.260, 4.360 and 4.420 GeV, while no signals of $e^{+}e^{-} \to \pi^{0} J/\psi$ are observed. The measured energy-dependent Born cross section for $e^{+}e^{-} \to \eta J/\psi$ shows an enhancement around 4.2~GeV. The measurement is compatible with an earlier measurement by Belle, but with a significantly improved precision.